Description of problem: [ 0.4] Downloading: http://libguestfs.org/download/builder/fedora-25.xz [ 1.1] Planning how to build this image [ 1.1] Uncompressing [ 10.3] Resizing (using virt-resize) to expand the disk to 30.0G [ 51.9] Opening the new disk [ 60.8] Setting a random seed [ 60.8] Setting the hostname: rawhide [ 60.8] Linking: /etc/systemd/system/tmp.mount -> /dev/null [ 60.9] Installing packages: fedora-repos-rawhide [ 125.0] Editing: /etc/yum.repos.d/fedora-rawhide.repo [ 125.0] Installing packages: bash dnf dnf-plugins-core emacs mlocate net-tools nfs-utils ntp sudo telnet virt-builder: warning: log file /tmp/builder.log: Guestfs.Error("download: call launch before using this function\n(in guestfish, don't forget to use the 'run' command)") (ignored) virt-builder: error: dnf -y install 'bash' 'dnf' 'dnf-plugins-core' 'emacs' 'mlocate' 'net-tools' 'nfs-utils' 'ntp' 'sudo' 'telnet': command exited with an error If reporting bugs, run virt-builder with debugging enabled and include the complete output: virt-builder -v -x [...] Version-Release number of selected component (if applicable): libguestfs-tools-c-1.36.2-1.fc25.x86_64 How reproducible: 100% Steps to Reproduce: Not exactly sure at the moment...
I don't have a reproducer, but I understand what's happening. The first 'dnf' command is killed by the appliance kernel oom-killer. That either kills the appliance or else makes the appliance unusable in some way, so when we try to download the builder.log file it fails as shown. The root cause is that dnf is somehow using loads more memory in Rawhide.
Closing as this appears to have been fixed in F26+ dnf.